Representative radical curable resins having hydroxyl groups may include, for example, vinyl ester resins (epoxy acrylates) obtained by reacting an epoxy resin with acrylic acid, methacrylic acid or the like. The vinyl ester resins have (meth)acrylate groups having radical polymerizability and thus can be heat cured or light cured. Therefore, they are broadly used as resins for UV offset printing ink or resins for synthetic marble.
However, the vinyl ester resins suffer from polymerization inhibition by oxygen during polymerization. Therefore, they may suffer insufficient curing when used in a thin film coating process such as for obtaining a thin coating.
For avoiding the polymerization inhibition of vinyl ester resins by oxygen, it has been proposed to introduce an allyl ether group. Specifically, for example, Japanese Unexamined Patent Publication No. 61-101518 (JP-A-61-101518) may be mentioned. However, by the technique of JP-A-61-101518, the copolymerizability of a (meth)acrylate group and an allyl ether group is not necessarily good, and when this technique is employed in a thin film coating process such as for obtaining a thin coating, the polymerization rate is not necessarily sufficient and insufficient curing may result.
Further, as radical curable resins other than the vinyl ester resins, there are commercially available ester compounds of a polyhydric alcohol such as trimethylolpropane di-(meth)acrylate or pentaerythritol tri-(math)acrylate and (meth)acrylic acid, containing partially retained hydroxyl groups. However, these compounds also suffer from polymerization inhibition by oxygen during polymerization and therefore, may suffer insufficient curing when used in a thin film coating process such as for obtaining a thin coating.
Epoxy resins are excellent resins having extensive uses for coating materials, electrical insulating materials, laminate structure materials, civil engineering and construction materials, adhesives and the like. In particularly, it is known that they have a good adhesion as coating materials. However, they have problems in that a long time is necessary for curing and an amine used as a curing agent is retained in a large amount so as to cause coloration of the cured products.
In order to solve these problems, it has been proposed to modify the epoxy resins, but other problems have arisen, as described above with respect to JP-A-61-101518. Therefore, polymerizable compounds having an improved polymerizability and a polymerizable composition containing such a polymerizable compound have been required.
In general, the epoxy resin is acknowledged to be “a generic term for compounds having two or more epoxy groups (oxylane ring) within one molecule” (see, “24 Epoxy Resin” of Engineering Plastic Jiten (Dictionary of Engineering Plastics), 1st ed., 1st imp., page 621, Gihodo (Dec. 15, 1988)). A representative epoxy resin shown here is a bisphenol A-diglycidyl ether produced by the condensation of bisphenol A and epichlorohydrin. Other than this, those having a relatively low molecular weight, where a glycidyl group is added to the terminal hydroxyl group of (poly)ethylene glycol or where a glycidyl group is added to the hydroxyl group of 1,6-hexanediol, are described as examples of the epoxy resin.
On the other hand, compounds having one epoxy group within one molecule, such as allyl glycidyl ether, phenyl glycidyl ether and cresol glycidyl ether (specifically, for example, ADEKAGLYCIDOL ED-529 (produced by Asahi Denka Kogyo K.K.)), are commercially available as diluents for the epoxy resin. In “24 Epoxy Resin, 1.2 Curing Reaction (2) Auxiliary Material” of Dictionary of Engineering Plastics, supra, page 635, it is stated that “Some of these reactive diluents are previously mixed with an epoxy resin and the mixture is commercially available as one grade of epoxy resin”.
Accordingly, in the present invention, the epoxy resin is defined as “a compound having at least one epoxy group” and not limited in the size of the molecular weight.